Announcements play an important role in communication services such as telephony services. Announcements are normally pre-recorded or machine-generated media. Machine-generated media can, for example, be generated with a text-to-speech function (a.k.a. speech synthesis) or text-to-image. The announcements may be generated in the communication network or by the remote user's switchboard or computer.
Usage examples of announcements from the communication network include:                Error messages when the command that the user has initiated cannot be completed. For example: when the caller has suppressed presentation of the phone number and the answerer has defined that he will not answer calls without seeing the phone number, then the system must present an error message to the caller.        When a user puts the session on hold, the system may play a message or music-on-hold to the other user.        In a conference call, the conference server may present an announcement when a new user enters or when a user leaves the session, for example: “John Smith has entered the meeting” and “John Smith has left the meeting”.        A user has a pre-paid subscription that is running empty. The operator can restrict the usage due to a low amount and wants to announce that at session start or during the session (it might be a very long session).        A method that is used more and more on the Internet is to present an image with a pin code (or password) on a web page. The image of the pin code is distorted so much that automatic text recognition systems should not be able to detect the pin code while it should still be possible for a clever human to read the letters and numbers. This is used instead of sending the corresponding pin code with an (insecure) e-mail.        
Usage examples of announcements from the answerer are:                A user calls a travel agency to book a ticket. The following scenario is likely:                    1. The user talks with a travel agent to find the best traveling option. In this step, the discussion is between two humans.            2. After deciding on the travel, the user is requested to key in his credit card number. This is a man-machine communication where the user hears pre-recorded or machine-generated messages and presses the telephone buttons (0-9) to insert his numbers. In this process the following sentence probable: “Key in your credit card number”, “You have entered: 1234 5678 9012 3456. If this is correct then press 1, if not then press 2.”, “Insert the expiration date of your credit card”, “You have entered: Jan. 1, 2007”. These sentences will be generated by the announcement server.            3. After keying in the credit card number and other required data, the session continues with the travel agent in order to decide on further travel options.            4. These steps may be repeated multiple times.                        A user calls a service desk or contact center to fix some problems after buying a new computer. The service desk uses a screening process to classify the problem before connecting to the call to a technician. In this screening process, the user has to answer questions like: “If your problem is software related then press ‘1’ and hash. If it is hardware related then press ‘2’. If it is unknown then press ‘3’”. After this screening process, the session will be put on hold and a waiting message is played to the user. The technician may answer the call and may interrupt the waiting message at any point in time.        
Traditionally, the generation of informational messages such as prompts and voice announcements has been performed by relatively simple Time Division Multiplexing (TDM) based announcement machines in circuit-switched systems, using conventional Pulse Code Modulation (PCM) or Adaptive Differential PCM (ADPCM) for encoding and decoding purposes. In modern and future communication systems, the conditions and requirements for handling announcements will change dramatically, and there is thus a general need to provide solutions for efficiently handling announcement media in such communication systems.